Comparison of coordinate measurement precision of different landmark types on human crania using a 3D laser scanner and a 3D digitiser: Implications for applications of digital morphometrics

Abstract

A total of 11 340 Cartesian coordinates of 42 homologous landmarks on five excavated human crania were recorded by three observers using a three-dimensional (3D) digitiser and computer models created with a 3D laser scanner. The aim was to compare the errors of the coordinate data of landmarks of different types recorded with these two techniques. The results showed that digitiser-based and 3D model-based coordinate measurements had overall standard deviations of, respectively, AE0.79 and AE1.05 mm. However, the 3D digitiser yielded the most precise coordinate data for landmarks defined primarily by biological criteria (Type I landmarks), while the 3D laser scanner models yielded the most precise coordinate data for landmarks defined primarily by geometric criteria (Type III landmarks). These findings are likely to influence the research design of future craniometric studies, as they indicate that the suitability of certain landmark types as reference points for geometric operations, such as partial Procrustes analysis, depends on the method by which they are measured. This information is particularly important for retrospective research or for combined databases such as FORDISC or CRANID, which may integrate different types of landmarks recorded by different researchers and/or instruments. Crania displaying poor preservation and surface discoloration yielded larger measurement errors, especially for the 3D model measurements. This is not surprising given that landmarks on 3D models cannot be located using tactile means, but have to be located solely on a visual basis. Nonetheless, even though the digitiser measurements exhibit an overall precision slightly greater than the 3D model measurements, both techniques yield coordinate data with a precision sufficient for most craniometric research.

Revisiting scoliosis in the KNM-WT 15000 Homo erectus skeleton

“…Like previous studies based on a MicroScribe or a similar coordinate measuring machine (Parent et al, 2002;von Cramon-Taubadel et al, 2007;Sholts et al, 2011), we found an average error of measurement of the 3D landmarks of about 0.5 mm. However, individual landmarks can have higher errors of measurement.…”

Accuracy and reliability of measurements obtained from computed tomography 3D volume rendered images

“…Because Type II and III landmarks present with lower precision compared to Type I landmarks [21,51,52], measurements inclusive of Type II and III landmarks were expected to result in lower repeatability. The measurements that presented with the highest intra-observer error were OBH defined by Type III landmarks, OBB defined by Type I and III landmarks, and DKB defined by Type I landmarks.…”

“…a 1 mm difference can account for upwards of 10% of the error) and because midshaft measurements are not defined by anatomic landmarks [21,50]. When measuring the skeletal elements on CT, the most difficult aspect is not being able to handle the remains.…”

“…Measurement error, both because of uncertainty in landmark identification/location and alterations in the objects true dimension as a consequence of imaging, has the potential to drastically affect the interpretation of results, thus this error should be considered in research design [20,21]. Furthermore, the Daubert guidelines emphasize the importance of precision, accuracy and reliability in forensic science research [20,[22][23][24].…”

The Suitability of 3D Data: 3D Digitisation of Human Remains

“…Nevertheless, significant errors have been found between data produced using different types of 3D digitisers (Ross and Williams 2008), indicating internal inconsistency within accuracy assessment methods. Digitisers have also been shown to result in relatively high differences in comparison with 3D CT methods (Richtsmeier 1995), and while some studies indicate they proThe Suitability of 3D Data: 3D Digitisation of Human Remains duce significantly more accurate results than 3D laser scans (Sholts et al 2011), others have found the two methods to be largely comparable (Algee-Hewitt and Wheat 2016). Further studies have indicated that the accuracy of results between data collection methods is dependent on the state of the material in question, with more tactile techniques where data can be collected directly from the object, such as traditional anthropometry and the use of 3D digitisers, generating more reliable and accurate results than virtual techniques for specimens affected by some kinds of taphonomic damage (Sholts et al 2011).…”